99 galant won't idle after battery disconnected and reconnected.

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Hi all,

I have a mitsubishi galant 99, 85xxx, 4 cyl, 2.4 Liter, auto transmission. Two days ago the battery was disconnected duo to a bad connection to the positive terminal, but I did't know it. Jump started it and drove to a nearby autozone and wanted to test the battery. Engine died just while I arrived at the autozone parking lot after a couple of miles driving. Tested battery. It was working fine! Then I started the car and wanted to test the charging system. Engine died quickly. Thought might be alternator problem. Next day, Luckly found that bad connection problem and fixed it. Cold started car, poor idle with 500~700 RPM (unstable). Engine died if no push on the gas pedal after it warmed up. Tested the charging system, working fine. Had to drive the car with right foot on gas and left foot on brake for 1.5 miles to a nearby mechanic shop. They scanned the on-board computer and probably reset the idle air control (IAC) valve or PCM. They said the computer might lose some data after battery was disconnected. I was charged $65 for that service. Now the car seems working fine. However, I still have two questions.

1. What should I do when I replace the battery next time? I don't want to pay another $65 to reset the computer.

2. I drove the car with two feet on that day since I had to put my right foot on the gas all the time. I remember the tachometer read about 1000 RPM with gear engaged while I waited before the traffic lights. I made about 6 stops totally. Each stop last about 5-30 seconds. I am wondering if this could harm the auto transmission since the normal idle speed is about 750 RPM with gear engaged.

Any input is welcome. I appreciate your help. Thanks.


posted by  shenbao

Your right the computer does lose the stored information when disconnected, but as far as i know u didnt have to pay 65$, the car would have relearned the stored information after various driving (city/highway) after a week of driving it woulda been back to normal) Well thats how it is with my car, not 100% sure about mitstbushi's, but it should work the same way.

posted by  speedy266

What you have is a classic case of the IAC sensor/system (Idle Air Control) losing data when the battery is disconnected. Eventually it should re-learn itself but with some cars, they are far more sensitive than others. I have had to drive a car up to 20 miles before prior to it being right again after a battery disconnect. Sometimes you can just nurse the accelerator pedal for a few minutes and you'll feel it starting to kick in and retune it's idle settings. Many car manufactures call that system the IAC system and some call it the AIS (Air injection system). In either case, all that does is inject air (oxygen) into the intake to allow for the correct idle mixture and rpm. If you've ever paid attention in a fuel injected vehicle particularly when they are being started from sitting overnight or "cold" you will notice that when you first fire the engine, it over revs what it normally idles at. This is an accompalation of several things, mainly the IAC system at work. Then the revs are steadily and slowly backed down to normal idle speed as it warms. Sounds to me like there is nothing wrong with you car other than you did not drive it for long enough to reset it after having no power running to the pcm to retain all those settings. What you experienced is not at all uncommon.

I am not really sure what to tell you about all the other stuff you posted about a "bad connection." To be honest I can't really follow you as to what the problem is. Just remember two things: On a good battery with a bad alternator, an engine will run for as long as the battery is good and until it sucks all the power from the battery. On a bad battery with a good alternator, once you have the engine running, you could drive it until you run out of gas, but if you shut it off, it won't recrank. Your problem all reads to me like you have an IAC problem. I am not aware of how you can "reset" the IAC valve other than to run the engine and allow the PCM to do it. If you hook the scanner up to the obd port, you can probably view the voltage at the sensor, but not sure if the software allows for a reset....maybe the dealer computer does....it's a powerful one. I have worked on many cars where I sat for an extended period and the IAC would not idle the engine correctly, so I'd disconnect and reconnect the battery again and then it would clear itself. I'd be curious how you "reset" the IAC.

P.S. Your transmission should be fine.

posted by  cmeseadoin

Hi guys :wink2:, thank you for your replies. Initially, the connection to the battery positive terminal was loose, I couldn't start the car. I thought it was a bad battery. But later on I found the problem and fixed it. However, the engine would still die after it started, I though it might be the alternator problem. Test the charging system. It working fine. I figured out the problem was that I had to put a foot on the gas pedal, otherwise engine would die. I think the mechanic probably pulled the fault code (or original data) that was dropped when the battery was disconnected and input it back to the computer for relearning process. It only took them for about 20-30 minutes to fix the problem.

Based on your replies, it seems that this is a common problem for the computer to lose data after the battery is disconnected and reconnected. Next time I am going to drive longer distance to let the computer relearn the necessary information if this problem ever happens again.

Again, I very much appreciate your replies!


posted by  shenbao

You're welcome......Just a dead battery should not set any fault codes. Now if the connection corroded and the computer sensed erratic reading from the electrical system, then I would think something else a little sketchy could have happened. The IAC would not set a code if there was not a functional problem with it, but who knows what happened. I still don' think the shope could have "reset the IAC." It think you paid money on that one that was purely bogus from the shop. They may have read the sensor data and watched it to make sure it is working but not "reset" it. According to what I know, you can't reset the IAC. If it is broken, you have to replace it or sometimes remove and clean it and it will work again. In any event, that can be tricky to reset. The best way to do it is drive the car for a while in a situation where you do not continuously stop at lights and intersections for a while. IE) interstate for 5-10 miles so that you constantly are applying accelerator pressure and not letting off it all the time. That may help with the computer re-learn process. :-) Glad you got it sorted out.

posted by  cmeseadoin

My nissan pulsar (1990 model n13) was doing exactly the same thing after totally draining the battery. After recharging the battery the car started fine and could be driven but stalled as soon as the revs dropped. I drove ten miles but it was still stalling. I was going to buy a new battery then the automotive electrician said "it sounds like your throttle body. Bring it down and I'll clean it out" (at a cost of course). I've never heard of a throttle body before and was willing to pay to have it repaired. Then my mate suggested 'Try Throttle Body Cleaner' a relatively cheap aerosol spray that works like carby cleaner or fuel injector cleaner (a solvent). It was a simple matter of removing the big rubber hose between the air cleaner and the 'throttle body'. Immediately after spraying the cleaner into the throttle body (it lays horizontal) all this black liquid started flowing out (I'm assuming carbon build up). I started the car and it was idling!!, I sprayed some more cleaner inside while twisting the throttle and I've save some hard earned money. A simple solution that I have not seen after searching many forums.

posted by  ray_c_yuen

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